docs: def p_expression(self, p):
          """expression : jsonpath
                        | jsonpath FILTER_OP ID
                        | jsonpath FILTER_OP FLOAT
                        | jsonpath FILTER_OP NUMBER
                        | jsonpath FILTER_OP BOOL
          """
          if len(p) == 2:
              left, op, right = p[1], None, None
          else:
              __, left, op, right = p
          p[0] = _filter.Expression(left, op, right)